For the last couple of days, as the ship moves toward Texas, we’ve encountered lots of sargassum. Sargassum is a type of macroalgae, or seaweed. Some types of sargassum are benthic; as you remember, this means they live and grow on the bottom of the ocean. Out here on the Oregon II, we’re seeing planktonic sargassum – the drifting kind – and lots of it. This sargassum drifts around the surface of the Gulf, thanks to the tiny, air-filled float pods all throughout its leaves. When pieces of sargassum meet up, they become entangled and start to drift together. Before long, vast blankets or mats of sargassum form. We’ve seen some impressive mats in the past few days, some almost as long as the ship itself!

Blanket of sargassum

Sargassum City

These mats create a bit of a challenge when it comes to dropping the nets. The Bongo Net and the Subsurface Neuston stay below the surface, so typically they don’t catch much sargassum, unless some slips in just as the nets enter or leave the water. However, the regular Neuston net stays on the surface for the duration of the drop. This is a perfect opportunity for sargassum to slide right in. Ideally, we want this net submerged for 10 minutes, but when the sargassum is thick, we have to cut this down to five. Even then, we’ve had as much as 30 gallons of sargassum show up in one drop.

You can find so much life in one handful of sargassum

When we get sargassum, we have to spray it off with sea water and sort through it to collect any plankton that are tangled in the leaves. This is quite a bit of work when we get a lot of sargassum, but I have come to really enjoy it because of the amazing little creatures that we find. A piece of sargassum can be like a little city, teeming with life, with a large variety of species. Many of these are big enough that you can easily see them with the naked eye. These sargassum communities contain everything that their residents need to survive, including a food web and plenty of shelter. It’s also a great lesson in adaptation. The animals that live in sargassum blend in so well that we have to look very carefully to find them. Most of them are either transparent, or they exactly match the color of the seaweed, and there are tons of nooks and crannies for hiding.

Here are just a few of the delightful little animals that we’ve found in the sargassum:

Sargassum fish: These little guys are pretty amazing. They look fairly harmless, but they are actually ambush predators. They have two small foot-like fins on their undersides, which they use to move around and perch in one place in the seaweed. When a smaller animal comes close, the sargassum fish open their mouths wide and suck the unsuspecting prey in, just like a vacuum cleaner. They’ll even eat other, smaller sargassum fish! Some of them even have a piece of flesh called an esca that dangles from their head, which they use as a lure to attract prey.

A large sargassum fish from a Neuston net. See the little pectoral fin “feet?”

This is the typical size for the sargassum fish that we’ve found (about one inch).

Sargassum swimming crabs: These tiny crabs are capable of walking on land, but they are also excellent swimmers, thanks to their paddle-shaped back legs. They are also ambush predators; they stalk smaller sargassum dwellers and give their prey a nasty jab to catch and kill them.

Sargassum swimming crab. See its paddle-shaped hind feet?

Sargassum nudibranch: Nudibranchs are a type of mollusk that have a shell in their juvenile stage, but lose the shell as they mature. Sargassum nudibranchs are so well camouflaged that we sometimes feel their soft bodies in the sargassum before we see them. They stay mainly in the sargassum, but if they happen to get washed out, they can flex their bodies back and forth to swim back to the seaweed. It’s really quite amazing to watch!

A little sargassum nudibranch. Looks like a blob here, but they are very graceful swimmers!

Challenge Yourself: Hey there, Nature Exchange traders! Can you think of an animal that blends into its environment in the Mojave Desert? What about a creature that is an ambush predator? Draw a picture or write down some facts and bring it in to the Nature Exchange for bonus points. Be sure to tell them that Emmi sent you!

Personal Log:

Yesterday, I saw some evidence of the impact that we have on our oceans. While sorting through some sargassum, I found a plastic ribbon with a balloon fragment attached wrapped around a piece of sargassum. We were hundreds of miles from shore when I found it. It was sad for me to see a piece of human trash tangled around this little sargassum community. I know it’s still pretty common for people to organize balloon releases to honor a special person or occasion, but I wonder if there might be another way to do so. Maybe instead of a balloon release, we can plant some trees, release ladybugs in a garden, organize a clean-up day at a local trail or park, etc. All of these things could impact the environment in a positive way. Just something to think about.

A piece of balloon and ribbon tangled up in the sargassum.

Now that I have adjusted to working the midnight to noon shift on the Oregon II, I am finding that I really enjoy it. In the past few days as we’ve approached a full moon, I’ve had the pleasure of seeing the moon reflect on the water, making it look like liquid mercury. For the first several days of this cruise, the sky was so dark that we could only see as far as the ship’s lights would allow, and maybe the distant lights from an oil rig or two. It was the darkest dark I’ve ever seen. Now, the moon lights up the sky enough that we can actually see the horizon. Then, a few hours into the shift, we get to watch the sun rise, which is spectacular every time. I’ve taken so many pictures of the sunrise, I can’t choose a favorite!

Sunrise on the Gulf of Mexico

We’re in the last few days of the survey, and we’ve taken the turn back east now. Until next time, be sure to track the Oregon II here: NOAA Ship Tracker